Electrostatic Discharge (ESD) is a rapid discharge that flows between two objects due to the built-up of static charge. ESD may destroy semiconductor devices because the rapid discharge can produce a relatively large current. In order to reduce the semiconductor failures due to ESD, ESD protection circuits have been developed to provide a current discharge path. When an ESD event occurs, the discharge current is conducted through the discharge path without going through the internal circuits to be protected.
In the semiconductor technology, resistor-capacitor (RC) triggered ESD protection circuits are widely used. An RC triggered ESD protection circuit may comprise a discharge transistor, a driver and an ESD spike detection circuit. The ESD spike detection circuit may include a resistance element and a capacitance element connected in series to form an RC detection circuit. The node between the resistance element and the capacitance element is coupled to the gate of the discharge transistor via the driver. The time constant formed by the resistance element and the capacitance element is so chosen that the discharge transistor is turned off when the ESD protection device operates in a normal power up mode. On the other hand, the discharge transistor is turned on when an ESD spike occurs at a power bus to which the ESD protection circuit is coupled. The turn-on of the discharge transistor may provide a bypass of the ESD current from the power bus to ground so as to clamp the voltage of the power bus to a level below the maximum rating voltage to which the internal circuit is specified, so that it helps to prevent the large voltage spike from damaging the internal circuits being protected.
In order to achieve a robust ESD protection and avoid false triggering, the RC time constant of a trigger circuit is chosen between the rise time of an ESD voltage spike and the rise time of a normal power up. When the RC time constant is not set correctly, the discharge transistor is turned on during a normal power up condition. Consequently, a leakage current may occur.
Power consumption has become an important performance index of semiconductor integrated circuits. The leakage current from ESD protection circuit may cause unnecessary power losses. By employing a low leakage current ESD protection circuit, the total power consumption of a semiconductor chip can be improved.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.